Standby Switches – Everything about them!

Should we use the standby switch?

In most tube guitar amplifiers, the standby switch is largely unnecessary. By now, the standby debate has been settled.

The accepted theory was standby switches were there to allow the tube heaters warm up before applying high voltage to the tubes. Failure to follow the power on – wait 45 seconds or more – turn off standby – rock out ritual meant that you were drastically reducing tube life by causing “cathode stripping” in the tubes.

Cathode stripping is a real thing; applying a high voltage to certain kinds of tube with a cold cathode will strip particles of the cathode off, which is as bad as it sounds.

However, cathode stripping doesn’t happen in the tubes that are commonly used in guitar amplifiers so there’s no need to wait for the heaters to warm up before applying the plate voltage.

The reality is modern guitar amplifiers generally have much more filtering in the high voltage supplies than there vintage counterparts, so the plate voltage in later stages comes up slowly over many seconds anyhow. In amps with tube rectifiers, the rectifier’s themselves start up slowly, but also their high resistance creates a long time constant with the main filter cap. Point being: tubes rarely, if ever, see the full B+ with dead-cold heaters.

For those of you that do use your standby switch, this is why it takes a while before the amp comes to life and volume gradually ramps up after flipping the switch. Most people think this is the heaters warming up; it’s not, it’s the plate voltage.

There’s actually potential for more harm done to the tubes by using the standby switch…this is caused by something called “cathode poisoning”. Cathode poisoning occurs when the cathode is heated in the absence of plate voltage for long periods of time. When poisoning occurs, the cathode’s chemical structure changes and it becomes less able to emit electrons. If the cathode becomes sufficiently ‘poisoned’, the tube will become noisy and its ability to amplify will suffer.

That said, I think the best approach for a solid answer to this question is to look deeper at why the standby switch is on your amp in the first place. The truth is…we have no clue.

The standby switch appears to have started with Fender, and appears to have been copied by Marshall, and then suddenly most guitar amps had them…but we can only speculate as to why.

Just because we’ve debunked the cathode stripping myth in modern times on the interwebs doesn’t a lone engineer didn’t misread or misunderstand something about tubes in the 1950’s. That’s just as plausible as the standby switch protects the filter capacitors, or provides a soft-start for amps with solid-state rectifiers, is really just a set-break switch, or any of the other theories as to why they are there. All good ideas, but all speculation.

It is safe to say the majority of the amplifier’s out there today have standby switches solely because of tradition & customer expectation. Standby switches are commonplace, so to not include one might seem weird to the player. It could also be that the designer doesn’t know or even care that the traditional standby is irrelevant…they could just like them for historical or aesthetic reasons.

I personally design our products with standby switches. Now, before you think I’m a hypocrite for just making a case seeming like it is better not to use the standby, our standby switches are completely different than the traditional designs.

Usually, the standby switch is wired between the B+ transformer winding and the rectifier and simply turns off the high voltage to the tubes.

The standby switch on our MGP-1A Modeling Guitar Preamplifier however does three things at once. First, we lower the heater voltage to about 60% of its normal voltage. This keeps the tubes warmed up, but completely eliminates the possibility of cathode poisoning. The B+ is also turned off, and we turn off our auxiliary supplies. We do this because these supplies are the biggest energy consumers in our products; we feel being energy-responsible is important these days.

So in our products the standby switch is actually designed to be used in the traditional way: short breaks. However in this case, you won’t be hurting your tubes, nor will you be using any more energy than is necessary to keep the unit ready to go.

So what should we do? To standby or not standby, that is the question…

It all depends.

Leaving the standby switch off (play mode) at all times is likely not going to hurt anything. Taking small set breaks and using the standby switch in the traditional way is likely not going to hurt anything either, since cathode poisoning takes hours to begin occurring. And even then, it’s not like you’ll leave your amp on standby for an hour and come back to dead tubes. This happens gradually…just don’t do it every day and expect your tubes to last.

If the standby switch was something that did enough damage to tubes to worry about, it wouldn’t have survived 60+ years.

Further, as guitar amp designs get more and more advanced, you may see a change in the way standby switches are implemented (like ours). You may even see them disappear altogether.

So a one size fits all answer here doesn’t work. What does – it’s always best to consult the manual or manufacturer and follow their recommendations as you can never know what a circuit is doing or the designer’s intentions just by observing the presence of a switch on the front panel.

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About the Author: Brian Rois is the brainiac behind Analog Amp Modeling. He is the founder and product designer at Black Widow Audio Designs and loves to talk gear with anyone. When not designing, he can be found making his world famous artisanal pizza, which is only world famous because family in England thinks “it’s OK”.

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